For me it was my A sister. She's always been a very mean, manipulative, bitter person with NPD anyway, but when she became a drunk to-boot, it was just too much. Her entire personality changed due to the brain dying off (from both the alcohol and the repeated falls/concussions). The doctors told me she probably would never be the same when she came out of her coma. I was around her maybe twice after that and have made the decision to go No Contact. She is just a horrible person and I choose not to be around the toxicity.
ETA: I was secretly hoping when she woke up she'd have become a NICER person. When I realized she hadn't, I said BUH-BYE.